Proteomic analysis of differentially expressed proteins in Lactobacillus brevis NCL912 under acid stress.

Protein expression of Lactobacillus brevis NCL912 under acid stress was analysed by two-dimensional gel electrophoresis and MS. Twenty-five proteins were differentially expressed under acid stress. Among them, eight protein spots were identified by matrix-assisted laser desorption/ionization time-of-flight MS, of which seven were upregulated and one was downregulated. The function of the downregulated protein was unknown and the putative functions of the upregulated proteins were categorized as stress response, DNA repair, protein synthesis and glycolysis. Quantitative real-time PCR was used to further validate these differentially expressed proteins at the mRNA level and a positive correlation between the content of the proteins and their mRNA levels was found. The results suggest that these proteins are involved in the acid stress response mechanisms of this bacterium.